The present invention relates to a full-mesh optical wavelength division multiplexing transmission network system for transmitting a plurality of wavelength-multiplexed optical signals between a plurality of transmitting/receiving apparatuses.
In an optical wavelength division multiplexing (WDM) transmission system for transmitting a plurality of optical signals through a single optical fiber by assigning different wavelengths to each optical signal, it is possible not only to remarkably increase the capacity of the transmission path, but also to perform the xe2x80x9cwavelength-addressingxe2x80x9d operation in which information about the addressee of the relevant signal corresponds to each wavelength itself.
A star-topology WDM system includes an arrayed-waveguide grating type multiplexing/demultiplexing circuit (or arrayed-waveguide grating type multi/demultiplexer) in the center of the system, where this multiplexing/demultiplexing circuit has a wavelength response having a cyclic input/output relationship, and makes it possible to connect N transmitting/receiving apparatuses with each other. According to such a star-type WDM system, it is possible to realize a full-mesh WDM transmission network system only by using optical signals of N wavelengths, in which each of Nxc3x97N signal paths for connecting the apparatuses with each other can be independently connected.
FIG. 4 is a schematic diagram showing the structure of a conventional full-mesh WDM transmission network system.
In the figure, reference numerals 1 to 7 indicate the 1st to Nth transmitting/receiving apparatuses (the 7th to (Nxe2x88x921)th apparatuses are not shown) for transmitting and receiving a WDM (wavelength-division-multiplexed) signal (of wavelengths xcex1 to xcexn), reference numeral 8 indicates an Nxc3x97N arrayed-waveguide grating type multiplexing/demultiplexing circuit (AWG) having N input and N output ports and having a wavelength response which has a cyclic input/output relationship.
FIG. 5 is a diagram showing the general structure of the full-mesh WDM transmission network system in FIG. 4.
In FIG. 5, reference numerals 9 to 12 indicate the 1st to Nth transmitting/receiving apparatuses (the ith apparatus indicates any of the omitted apparatuses in the figure), reference numeral 13 indicates a receiver for receiving a WDM signal (of wavelengths xcex1 to xcexn), reference numeral 14 indicates a transmitter for transmitting a WDM signal (of wavelengths xcex1 to xcexn), reference numeral 15 indicates a demultiplexer for demultiplexing a WDM signal transmitted through a single optical fiber, reference numeral 16 indicates a multiplexer for multiplexing a plurality of optical signals having different wavelengths transmitted from the transmitter 14 so as to transmit a signal through a single optical fiber, reference numeral 17 indicates an Nxc3x97N arrayed-waveguide grating type multiplexing/demultiplexing circuit (AWG), and reference numerals 18 to 21 indicate optical fibers for optically connecting the transmitting/receiving apparatuses 9 to 12 and the input and output ports of AWG 17. Here, the structure of each transmitting/receiving apparatus (10 to 12) is the same as the transmitting/receiving apparatus 9.
FIG. 6 is a diagram showing the wavelength response having a cyclic input/output relationship, and the connection relationship between the transmitting/receiving apparatuses and the AWG ports in the conventional full-mesh WDM transmission network system. For a simple explanation, the case using an 8xc3x978 AWG is shown in FIG. 6.
Between 8 input ports and 8 output ports of the AWG, (8xc3x978=) 64 paths can be established; however, the cyclic characteristic as shown in FIG. 6 makes it possible to independently establish 64 paths using the minimum 8 wavelengths. The above input and output ports of the AWG are connected to each relevant transmitting/receiving apparatus, so that each signal can be independently transmitted via any possible path between the eight transmitting/receiving apparatuses. Here, a specific wavelength xcexi is assigned to each path. Therefore, it is possible to perform the wavelength addressing operation in which when the wavelength corresponding to a target receiver is selected at the transmitter side, a signal is automatically transmitted to the target receiver.
FIG. 7 is a diagram for explaining the wavelength addressing operation. In the figure, reference numerals 22 to 29 indicate 8 transmitting/receiving apparatuses, and reference numeral 30 indicates an 8xc3x978 AWG. The wavelength response of the AWG and the connection relationship between the AWG ports and each transmitting/receiving apparatus are the same as those shown in FIG. 6.
The optical signal of wavelength xcex7 transmitted from the 1st transmitting/receiving apparatus 22 is introduced to input port 1 of AWG 30, and is output from output port 2 to the 2nd transmitting/receiving apparatus by switching the optical signal in the AWG 30 according to its wavelength. Similarly, the response signal of wavelength xcex7 transmitted from the 2nd transmitting/receiving apparatus 23 is transmitted to the 1st transmitting/receiving apparatus 22 via AWG 30. In addition, the optical signals having wavelengths xcex2 and xcex8 are respectively and automatically transmitted to the 5th transmitting/receiving apparatus 26 and the 3rd transmitting/receiving apparatus 24.
However, in the above conventional full-mesh WDM transmission network system, the addressee of the target signal one-to-one corresponds to a wavelength; therefore, if the transmitter relating to the relevant wavelength or the semiconductor laser used as a light source is damaged, a signal cannot be transmitted to a target receiver. Also if the receiver relating to the relevant wavelength is damaged, a similar problem occurs. These problems are serious for suitably operating and managing the system. Furthermore, in a conventional system, it is impossible to temporarily increase the transmission capacity between specific transmitting/receiving apparatuses.
In consideration of the above problems, an objective of the present invention is to provide a full-mesh optical wavelength division multiplexing transmission network system for suitably coping with a damaged transmitter or receiver corresponding to a specific wavelength, and for temporarily increasing the transmission capacity between specific transmitting/receiving apparatuses in case of need.
To achieve the above objective, the present invention provides an optical wavelength division multiplexing transmission network system comprising:
an arrayed-waveguide grating type multiplexing/demultiplexing circuit having N input ports and N output ports, where N is a plural number; and
N transmitting/receiving apparatuses, each apparatus being optically connected to a predetermined input port and a predetermined output port of the arrayed-waveguide grating type multiplexing/demultiplexing circuit, wherein:
the arrayed-waveguide grating type multiplexing/demultiplexing circuit has a wavelength response having a cyclic input/output relationship; and
each transmitting/receiving apparatus comprises:
a demultiplexer for demultiplexing an optical signal input from the predetermined output port of the arrayed-waveguide grating type multiplexing/demultiplexing circuit into signals of N wavelengths, and respectively outputting the demultiplexed optical signals from N output ports;
a transmitter for respectively transmitting optical signals of N wavelengths from N output ports;
a receiver for respectively receiving optical signals of N wavelengths from N input ports;
a multiplexer for multiplexing optical signals of N wavelengths input from N input ports, and outputting the multiplexed signal to the predetermined input port of the arrayed-waveguide grating type multiplexing/demultiplexing circuit; and
N 2-input and 2-output optical path switching elements corresponding to N wavelengths, each switching element being independently switched between first and second connective conditions, wherein:
in the first connective condition, the output port corresponding to a specific wavelength of the demultiplexer is connected to the input port corresponding to the specific wavelength of the receiver, and the output port corresponding to a specific wavelength of the transmitter is connected to the input port corresponding to the specific wavelength of the multiplexer; and
in the second connective condition, the output port corresponding to a specific wavelength of the transmitter is connected to the input port corresponding to the specific wavelength of the receiver, and the output port corresponding to a specific wavelength of the demultiplexer is connected to the input port corresponding to the specific wavelength of the multiplexer.
According to the present invention, an optical signal transmitted to the demultiplexer of a relevant transmitting/receiving apparatus via the switching operation of the arrayed-waveguide grating type multiplexing/demultiplexing circuit according to the wavelength of the optical signal can be returned by using the relevant 2-input and 2-output optical path switching element in the transmitting/receiving apparatus so that the returned signal is transmitted via the multiplexer to the arrayed-waveguide grating type multiplexing/demultiplexing circuit again. This optical signal is re-switched in the arrayed-waveguide grating type multiplexing/demultiplexing circuit according to the wavelength, and is transmitted to another transmitting/receiving apparatus.
That is, when an optical signal is transmitted from the transmitter of one of the transmitting/receiving apparatuses to (the receiver of) a target transmitting/receiving apparatus (i.e., addressee), even if the transmitting or receiving portion corresponding to the relevant Wavelength is damaged, an optical signal can be bypassed and transmitted to the target receiver by (repeatedly) performing the signal-returning operation as explained above.
In addition, according to the above structure, a plurality of signal paths can be temporarily established between specific transmitting/receiving apparatuses by switching the connective condition of each 2-input and 2-output optical path switching element, thereby temporarily increasing the transmission capacity.
As a preferable example, in the connection between the arrayed-waveguide grating type multiplexing/demultiplexing circuit and the transmitting/receiving apparatuses, the ith input port and the (Nxe2x88x92i+1)th output port of the arrayed-waveguide grating type multiplexing/demultiplexing circuit are respectively connected to the multiplexer and the demultiplexer of the ith transmitting/receiving apparatus via an optical fiber, where i is an integer from 1 to N.
In addition, each of the N 2-input and 2-output optical path switching elements may be a thermo-optic switch using the thermo-optic effect of a silica-based planar lightwave circuit.